User Photo/Company Logo:
This image is used as your logo in emails, receipts, your embedded checkout and on your enhanced Outdoorsy Profile.
Cover photo:
This is the primary background image displayed on your profile and checkout pages
The sizes for the company logo/user photo & the cover photo are as follows:
Company Logo: 500 x 500
Cover Photo: 300 x 1400
Those can be changed in Account Settings > About My Business

Listing Photo
The optimal size for listing photos (photos of the RV) is: 1024 X 800
Listing Photo: 1024 x 800
Pro tip: Photos including "happy campers" are proven to increase conversion!
Disclaimer: Make sure to respect the local laws surrounding photo privacy.